Current state of the art propellant-based downhole stimulation employs only one ballistic option, in the form of a right circular cylinder of a single type of propellant grain, which may comprise a single volume or a plurality of propellant “sticks” in a housing and typically having an axially extending hole through the center of the propellant through which a detonation cord extends, although it has been known to wrap the detonation cord helically around the propellant grain. When deployed in a wellbore adjacent a producing formation, the detonation cord is initiated and gases from the burning propellant grain exit the housing at select locations, entering the producing formation. The pressurized gas may be employed to fracture a formation, to perforate the formation when spatially directed through apertures in the housing against the wellbore wall, or to clean existing fractures or perforations made by other techniques, in any of the foregoing cases increasing the effective surface area of producing formation material available for production of hydrocarbons. In conventional propellant-based stimulation, due to the use of a single, homogeneous propellant and centralized propellant initiation, only a single ballistic trace in the form of a gas pressure pulse from propellant burn may be produced.
U.S. Pat. Nos. 7,565,930, 7,950,457 and 8,186,435 to Seekford, the disclosure of each of which is incorporated herein in its entirety by this reference, propose a technique to alter an initial surface area for propellant burning, but this technique cannot provide a full regime of potentially available ballistics for propellant-induced stimulation in a downhole environment. It would be desirable to provide enhanced control of not only the initial surface area (which alters the initial rise rate of the gas pulse, or dP/dt, responsive to propellant ignition), but also the duration and shape of the remainder of the pressure pulse introduced by the burning propellant.